Desalination, desalinization, and desalinisation refer to any of several processes that remove some amount of salt and other minerals from saline water. More generally, desalination may also refer to the removal of salts and minerals,[1] as in soil desalination, which also happens to be a major issue for agricultural production.[2]

Salt water is desalinated to produce fresh water suitable for human consumption or irrigation. One potential byproduct of desalination is salt. Desalination is used on many seagoing ships and submarines. Most of the modern interest in desalination is focused on developing cost-effective ways of providing fresh water for human use. Along with recycled wastewater, this is one of the few rainfall-independent water sources.[3]

Due to relatively high energy consumption, the costs of desalinating sea water are generally higher than the alternatives (fresh water from rivers or groundwater, water recycling and water conservation), but alternatives are not always available and rapid overdraw and depletion of reserves is a critical problem worldwide. Quoting Christopher Gasson of Global Water Intelligence, At the moment, around 1% of the world’s population are dependent on desalinated water to meet their daily needs, but by 2025, the UN expects 14% of the world’s population to be encountering water scarcity. Unless people get radically better at water conservation, the desalination industry has a very strong future indeed.[4]

Desalination is particularly relevant to dry countries such as Australia, which traditionally have relied on collecting rainfall behind dams to provide their drinking water supplies. According to the International Desalination Association, in June 2011, 15,988 desalination plants operated worldwide, producing 66.5 million cubic meters per day, providing water for 300 million people.[5] This number has been updated to 78.4 million cubic meters by 2013.,[4] or 57% greater than just 5 years prior. The single largest desalination project is Ras Al Khair in Saudi Arabia, which produces 1,025,000 cubic meters per day in 2014[4] The largest percent of desalinated water used in any country is in Israel, which produces 40% of its domestic water use from seawater desalination.[6]

The traditional process used in these operations is vacuum distillation—essentially the boiling of water at less than atmospheric pressure and thus a much lower temperature than normal. This is because the boiling of a liquid occurs when the vapor pressure equals the ambient pressure and vapor pressure increases with temperature. Thus, because of the reduced temperature, low-temperature "waste" heat from electrical power generation or industrial processes can be used.

Reverse osmosis desalination plant in Barcelona, Spain

The principal competing processes use membranes to desalinate, principally applying reverse osmosis technology.[7] Membrane processes use semipermeable membranes and pressure to separate salts from water. Reverse osmosis plant membrane systems typically use less energy than thermal distillation, which has led to a reduction in overall desalination costs over the past decade. Desalination remains energy intensive, however, and future costs will continue to depend on the price of both energy and desalination technology.

Energy consumption of sea water desalination can be as low as 3 kWh/m3,[8] including pre-filtering and ancillaries, similar to the energy consumption of existing fresh water supplies transported over large distances,[9] but much higher than local fresh water supplies which use 0.2 kWh/m3 or less.[10]

The laws of physics determine a minimum energy consumption for sea water desalination around 1 kWh/m3,[11][12] excluding pre-filtering and intake/outfall pumping. Under 2 kWh/m3[13] has been achieved with existing reverse osmosis membrane technology, leaving limited scope for further energy reductions.

Supplying all domestic water by sea water desalination would increase the United States' energy consumption by around 10%, about the amount of energy used by domestic refrigerators.[14]

Note: "Electrical equivalent" refers to the amount of electrical energy which could be generated using a given quantity of thermal energy and appropriate turbine generator. In addition, these calculations do not include the energy required to construct or refurbish consumable items used up in the processes.

Cogeneration is the process of using excess heat from electricity generation for another task: in this case the production of potable water from seawater or brackish groundwater in an integrated, or "dual-purpose", facility where a power plant provides the energy for desalination. Alternatively, the facility's energy production may be dedicated to the production of potable water (a stand-alone facility), or excess energy may be produced and incorporated into the energy grid (a true cogeneration facility). Cogeneration takes various forms, and theoretically any form of energy production could be used. However, the majority of current and planned cogeneration desalination plants use either fossil fuels or nuclear power as their source of energy. Most plants are located in the Middle East or North Africa, which use their petroleum resources to offset limited water resources. The advantage of dual-purpose facilities is they can be more efficient in energy consumption, thus making desalination a more viable option for drinking water.[16][17]

The Shevchenko BN350, a nuclear-heated desalination unit

In a December 26, 2007, opinion column in The Atlanta Journal-Constitution, Nolan Hertel, a professor of nuclear and radiological engineering at Georgia Tech, wrote, "... nuclear reactors can be used ... to produce large amounts of potable water. The process is already in use in a number of places around the world, from India to Japan and Russia. Eight nuclear reactors coupled to desalination plants are operating in Japan alone, nuclear desalination plants could be a source of large amounts of potable water transported by pipelines hundreds of miles inland..."[18]

Additionally, the current trend in dual-purpose facilities is hybrid configurations, in which the permeate from a reverse osmosis desalination component is mixed with distillate from thermal desalination. Basically, two or more desalination processes are combined along with power production. Such facilities have already been implemented in Saudi Arabia at Jeddah and Yanbu.[19]

A typical aircraft carrier in the US military uses nuclear power to desalinate 400,000 US gallons (1,500,000 l; 330,000 imp gal) of water per day.[20]

Costs of desalinating sea water (infrastructure, energy and maintenance) are generally higher than the alternatives (fresh water from rivers or groundwater, water recycling and water conservation), but alternatives are not always available. Achievable costs in 2013 range from 0.45 to 1 US$/cubic metre (2 to 4 US$/kgal). (1 cubic meter is about 264 gallons.)

The cost of untreated fresh water in the developing world can reach 5 US$/cubic metre.[21]

Average water consumption and cost of supply by sea water desalination (±50%)

Area

Consumption USgal/person/day

Consumption litre/person/day

Desalinated Water Cost US$/person/day

USA

100

378

0.29

Europe

50

189

0.14

Africa

15

57

0.05

UN recommended minimum

13

49

0.04

Factors that determine the costs for desalination include capacity and type of facility, location, feed water, labor, energy, financing, and concentrate disposal. Desalination stills now control pressure, temperature and brine concentrations to optimize efficiency. Nuclear-powered desalination might be economical on a large scale.[22][23]

While noting costs are falling, and generally positive about the technology for affluent areas in proximity to oceans, a 2004 study argued, "Desalinated water may be a solution for some water-stress regions, but not for places that are poor, deep in the interior of a continent, or at high elevation. Unfortunately, that includes some of the places with biggest water problems.", and, "Indeed, one needs to lift the water by 2,000 metres (6,600 ft), or transport it over more than 1,600 kilometres (990 mi) to get transport costs equal to the desalination costs. Thus, it may be more economical to transport fresh water from somewhere else than to desalinate it. In places far from the sea, like New Delhi, or in high places, like Mexico City, high transport costs would add to the high desalination costs. Desalinated water is also expensive in places that are both somewhat far from the sea and somewhat high, such as Riyadh and Harare. In many places, the dominant cost is desalination, not transport; the process would therefore be relatively less expensive in places like Beijing, Bangkok, Zaragoza, Phoenix, and, of course, coastal cities like Tripoli."[24] After being desalinated at Jubail, Saudi Arabia, water is pumped 200 miles (320 km) inland through a pipeline to the capital city of Riyadh.[25] For coastal cities, desalination is increasingly viewed as an untapped and unlimited water source.

In 2014, the Israeli cities of Hadera, Palmahim, Ashkelon, and Sorek were desalinizing water for less than 40 U.S. cents per cubic meter.[26] As of 2006, Singapore was desalinating water for US$0.49 per cubic meter.[27] The city of Perth began operating a reverse osmosis seawater desalination plant in 2006, and the Western Australian government announced a second plant will be built to serve the city's needs.[28] A desalination plant is now operating in Australia's largest city, Sydney,[29] and the Wonthaggi desalination plant was under construction in Wonthaggi, Victoria.

In December 2007, the South Australian government announced it would build a seawater desalination plant for the city of Adelaide, Australia, located at Port Stanvac. The desalination plant was to be funded by raising water rates to achieve full cost recovery.[32][33] An online, unscientific poll showed nearly 60% of votes cast were in favor of raising water rates to pay for desalination.[34]

A January 17, 2008, article in the Wall Street Journal stated, "In November, Connecticut-based Poseidon Resources Corp. won a key regulatory approval to build the $300 million water-desalination plant in Carlsbad, north of San Diego. The facility would produce 50,000,000 US gallons (190,000,000 l; 42,000,000 imp gal) of drinking water per day, enough to supply about 100,000 homes ... Improved technology has cut the cost of desalination in half in the past decade, making it more competitive ... Poseidon plans to sell the water for about $950 per acre-foot [1,200 cubic meters (42,000 cu ft)]. That compares with an average [of] $700 an acre-foot [1200 m³] that local agencies now pay for water."[35] In June 2012, new estimates were released that showed the cost to the water authority had risen to $2,329 per acre-foot.[36] Each $1,000 per acre-foot works out to $3.06 for 1,000 gallons, or $.81 per cubic meter.[37]

While this regulatory hurdle was met, Poseidon Resources is not able to break ground until the final approval of a mitigation project for the damage done to marine life through the intake pipe is received, as required by California law. Poseidon Resources has made progress in Carlsbad, despite an unsuccessful attempt to complete construction of Tampa Bay Desal, a desalination plant in Tampa Bay, FL, in 2001. The Board of Directors of Tampa Bay Water was forced to buy Tampa Bay Desal from Poseidon Resources in 2001 to prevent a third failure of the project. Tampa Bay Water faced five years of engineering problems and operation at 20% capacity to protect marine life, so stuck to reverse osmosis filters prior to fully using this facility in 2007.[38]

In the United States, cooling water intake structures are regulated by the Environmental Protection Agency under Section 316(b) of the Clean Water Act. These intake structures can have the same impacts to the environment as desalination facility intakes. According to the EPA, water intake structures cause adverse environmental impact by pulling large numbers of fish and shellfish or their eggs into an industrial system. There, the organisms may be killed or injured by heat, physical stress, or chemicals. Larger organisms may be killed or injured when they are trapped against screens at the front of an intake structure.[41] Alternative intake types which avoid this environmental impact include beach wells, but these require more energy and higher costs, while limiting output.[42]

All desalination processes produce large quantities of a concentrate, which may be increased in temperature, and contain residues of pretreatment and cleaning chemicals, their reaction byproducts, and heavy metals due to corrosion.[44] Chemical pretreatment and cleaning are a necessity in most desalination plants, which typically includes the treatment against biofouling, scaling, foaming and corrosion in thermal plants, and against biofouling, suspended solids and scale deposits in membrane plants.[45]

To limit the environmental impact of returning the brine to the ocean, it can be diluted with another stream of water entering the ocean, such as the outfall of a wastewater treatment or power plant. While seawater power plant cooling water outfalls are not as fresh as wastewater treatment plant outfalls, salinity is reduced. With medium to large power plant and desalination plant, the power plant's cooling water flow is likely to be at least several times larger than that of the desalination plant. Another method to reduce the increase in salinity is to mix the brine via a diffuser in a mixing zone. For example, once the pipeline containing the brine reaches the sea floor, it can split into many branches, each releasing brine gradually through small holes along its length. Mixing can be combined with power plant or wastewater plant dilution.

Brine is denser than seawater due to higher solute concentration. The ocean bottom is most at risk because the brine sinks and remains there long enough to damage the ecosystem. Careful reintroduction can minimize this problem. For example, for the desalination plant and ocean outlet structures to be built in Sydney from late 2007, the water authority stated the ocean outlets would be placed in locations at the seabed that will maximize the dispersal of the concentrated seawater, such that it will be indistinguishable beyond between 50 and 75 meters (164 and 246 ft) from the outlets. Typical oceanographic conditions off the coast allow for rapid dilution of the concentrated byproduct, thereby minimizing harm to the environment.

Some methods of desalination, particularly in combination with evaporation ponds, solar stills, and condensation trap (solar desalination), do not discharge brine. They do not use chemicals in their processes nor the burning of fossil fuels. They do not work with membranes or other critical parts, such as components that include heavy metals, thus do not cause toxic waste (and high maintenance).

A new approach that works like a solar still, but on the scale of industrial evaporation ponds is the integrated biotectural system.[46] It can be considered "full desalination" because it converts the entire amount of saltwater intake into distilled water. One of the unique advantages of this type of solar-powered desalination is the feasibility for inland operation. Standard advantages also include no air pollution from desalination power plants and no temperature increase of endangered natural water bodies from power plant cooling-water discharge. Another important advantage is the production of sea salt for industrial and other uses. Currently, 50% of the world's sea salt production still relies on fossil energy sources.[citation needed]

Increased water conservation and efficiency remain the most cost-effective priorities in areas of the world where there is a large potential to improve the efficiency of water use practices.[47] Wastewater reclamation for irrigation and industrial use provides multiple benefits over desalination.[48] Urban runoff and storm water capture also provide benefits in treating, restoring and recharging groundwater.[49]

A proposed alternative to desalination in the American Southwest is the commercial importation of bulk water from water-rich areas either by very large crude carriers converted to water carriers, or via pipelines. The idea is politically unpopular in Canada, where governments imposed trade barriers to bulk water exports as a result of a claim filed in 1999 under Chapter 11 of the North American Free Trade Agreement (NAFTA) by Sun Belt Water Inc., a company established in 1990 in Santa Barbara, California, to address pressing local needs due to a severe drought in that area.[50]

Israeli researchers have found possible link between Seawater desalination and iodine deficiency. Their study, conducted by Yaniv Ovadia, registered dietitian, by the supervision of Dr Dov Gefel and Dr Aron M Troen from the Barzilai Medical center Ashkelon and the Hebrew University Jerusalem,[51] revealed prevalent, apparent Iodine Deficiency among euthyroid adults exposed to iodine-poor water[52] simultaneously with supply of an ever-increasing SWRO proportion of their area's drinking water. These researchers underscored the need for reliable data on iodine intake and status to illuminate the implications of SWRO desalination on health for populations in regions that are increasingly dependent on desalinated-water.[53]

Diesel generators are commonly used to provide electricity in remote areas. They typically produce about 40%-50% of the energy as low-grade heat which leaves the engine via the exhaust. By connecting a membrane distillation system to the diesel engine exhaust it is possible to use this low-grade heat which is currently wasted. Furthermore, the membrane distillation system actively cools the diesel generator, improving its efficiency and hence increasing its electricity output. This results in an energy-neutral desalination solution. An example of such a desalination plant was commissioned by Dutch company Aquaver in March 2014 in the island of Gulhi, Maldives.[54][55]

Originally stemming from ocean thermal energy conversion research, low-temperature thermal desalination (LTTD) takes advantage of water boiling at low pressures, potentially even at ambient temperature. The system uses vacuum pumps to create a low-pressure, low-temperature environment in which water boils at a temperature gradient of 8–10 °C (46–50 °F) between two volumes of water. Cooling ocean water is supplied from depths of up to 600 m (2,000 ft). This cold water is pumped through coils to condense the water vapor. The resulting condensate is purified water. LTTD may also take advantage of the temperature gradient available at power plants, where large quantities of warm wastewater are discharged from the plant, reducing the energy input needed to create a temperature gradient.[56]

Experiments were conducted in the US and Japan to test the approach. In Japan, a spray-ﬂash evaporation system was tested by Saga University.[57] In Hawaii, the National Energy Laboratory tested an open-cycle OTEC plant with fresh water and power production using a temperature difference of 20 C° between surface water and water at a depth of around 500 m (1,600 ft). LTTD was studied by India's National Institute of Ocean Technology (NIOT) from 2004. Their first LTTD plant opened in 2005 at Kavaratti in the Lakshadweep islands. The plant's capacity is 100,000 L (22,000 imp gal; 26,000 US gal)/day, at a capital cost of INR 50 million (€922,000). The plant uses deep water at a temperature of 7 to 15 °C (45 to 59 °F).[58] In 2007, NIOT opened an experimental, floating LTTD plant off the coast of Chennai, with a capacity of 1,000,000 L (220,000 imp gal; 260,000 US gal)/day. A smaller plant was established in 2009 at the North Chennai Thermal Power Station to prove the LTTD application where power plant cooling water is available.[56][59][60]

In October 2009, Saltworks Technologies, a Canadian firm, announced a process that uses solar or other thermal heat to drive an ionic current that removes all sodium and chlorine ions from the water using ion-exchange membranes.[61]

One such process was commercialized by Modern Water PLC using forward osmosis, with a number of plants reported to be in operation.[62][63][64]

The United States, France and the United Arab Emirates are working to develop practical solar desalination.[65] AquaDania's WaterStillar has been installed at Dahab, Egypt, and in Playa del Carmen, Mexico. In this approach, a solar thermal collector measuring two square metres can distill from 40 to 60 litres per day from any local water source - five times more than conventional stills and eliminating the need for polluting plastic PET bottles or tranportation of water supply.[66] In Central California, a startup company WaterFX is developing a solar-powered method of desalination that can enable the use of local water, including runoff water that can be treated and used again. Salty groundwater in the region would be treated to become freshwater, and in areas near the ocean, seawater could be treated.[67]

The Passarell process uses reduced atmospheric pressure rather than heat to drive evaporative desalination. The pure water vapor generated by distillation is then compressed and condensed using an advanced compressor. The compression process improves distillation efficiency by creating the reduced pressure in the evaporation chamber. The compressor centrifuges the pure water vapor after it is drawn through a demister (removing residual impurities) causing it to compress against tubes in the collection chamber. The compression of the vapor causes its temperature to increase. The heat generated is transferred to the input water falling in the tubes, causing the water in the tubes to vaporize. Water vapor condenses on the outside of the tubes as product water. By combining several physical processes, Passarell enables most of the system's energy to be recycled through its subprocesses, namely evaporation, demisting, vapor compression, condensation, and water movement within the system.[68]

Nanotube membranes may prove to be effective for water filtration and desalination processes that would require substantially less energy than reverse osmosis.[69]

Hermetic, sulphonated nano-composite membranes have shown to be capable of cleaning most all forms of contaminated water to the 'parts per billion' level. These nano-materials, using a non-reverse osmosis process, have little or no susceptibility to high salt concentration levels.[70][71][72]

On June 23, 2008, Siemens Water Technologies announced technology based on applying electric fields that purports to desalinate one cubic meter of water while using only 1.5 kWh of energy. If accurate, this process would consume only one-half the energy of other processes.[74] Currently, Oasis Water, which developed the technology, still uses three times that much energy. Researchers at the university of Texas at Austin and the University of Marburg are developing more efficient methods of electrochemically mediated seawater desalination.[75]

Membraneless desalination at ambient temperature and pressure using electrokinetic shocks waves has been demonstrated.[76] In this technique anions and cations in salt water are exchanged for carbonate anions and calcium cations respectively using electrokinetic shockwaves. Calcium and carbonate ions then react to form calcium carbonate, which then precipitates leaving behind fresh water. Theoretical energy efficiency of this method is on par with electrodialysis and reverse osmosis.

In 2009, Lux Research estimated the worldwide desalinated water supply will triple between 2008 and 2020.[77]

Estimates vary widely between 15,000-20,000 desalination plants producing more than 20,000 m3/day. Micro desalination plants are in operation nearly every where there is a natural gas or fracking facility in the United States.

The Millenium Drought (1997–2009) led to a water supply crisis across much of the country. A combination of increased water usage and lower rainfall/drought in Australia caused state governments to turn to desalination. As a result several large-scale desalination plants were constructed (see list).

Large-scale seawater reverse osmosis plants (SWRO) now contribute to the domestic water supplies of several major Australian cities including Adelaide, Melbourne, Sydney, Perth and the Gold Coast. While desalination helped secure water supplies, it is energy intensive (≈$140/ML) and has a high carbon footprint due to Australia's coal-based energy supply.[citation needed] In 2010, a Seawater Greenhouse went into operation in Port Augusta.[82][83][84]

A growing number of smaller scale SWRO plants are used by the oil and gas industry (both on and offshore), by mining companies to supply slurry pipelines for the transport of ore and on offshore islands to supply tourists and residents.

Completed in 2000, the Al Hidd Desalination Plant on Muharraq island employed a multistage flash process, and produces 272,760 m3 (9,632,000 cu ft) per day.[85] The Al Hidd distillate forwarding station provides 410 million liters of distillate water storage in a series of 45-million-liter steel tanks. A 135-million-liters/day forwarding pumping station sends flows to the Hidd, Muharraq, Hoora, Sanabis, and Seef blending stations, and which has an option for gravity supply for low flows to blending pumps and pumps which forward to Janusan, Budiya and Saar.[86]

Upon completion of the third construction phase, the Durrat Al Bahrain seawater reverse osmosis (SWRO) desalination plant was planned to have a capacity of 36,000 cubic meters of potable water per day to serve the irrigation needs of the Durrat Al Bahrain development.[87] The Bahrain-based utility company, Energy Central Co contracted to design, build and operate the plant.[88]

China operates the Beijing Desalination Plant in Tianjin, a combination desalination and coal-fired power plant designed to alleviate Tianjin's critical water shortage. Though the facility has the capacity to produce 200,000 cubic meters of potable water per day, it has never operated at more than one-quarter capacity due to difficulties with local utility companies and an inadequate local infrastructure.[90]

The HK Water Supplies Department had pilot desalination plants in Tuen Mun and Ap Lei Chau using reverse osmosis technology. The production cost was at HK$7.8 to HK$8.4 /m3.[99][100] In 2011, the government announced a feasibility study whether to build a desalination plant in Tseung Kwan O.[101] Hong Kong used to have a desalination plant in Lok On Pai.[102]

An assumption is that around 400,000 m3/d of historic and newly installed capacity is operational in Iran.[106] In terms of technology, Iran's existing desalination plants use a mix of thermal processes and RO. MSF is the most widely used thermal technology although MED and vapour compression (VC) also feature.[106]

Israel Desalination Enterprises' Sorek Desalination Plant in Palmachim provides up to 26,000 m³ of potable water per hour (2.300 m³ p.a.). At full capacity, it is the largest desalination plant of its kind in the world.[107] Once unthinkable, given Israel's history of drought and lack of available fresh water resource, with desalination, Israel can now actually produce a surplus of fresh water.[108]

The Hadera seawater reverse osmosis (SWRO) desalination plant in Israel is the largest of its kind in the world.[109][110] The project was developed as a build–operate–transfer by a consortium of two Israeli companies: Shikun and Binui, and IDE Technologies.[111]

By 2014, Israel's desalination programs provided roughly 35% of Israel's drinking water and it is expected to supply 40% by 2015 and 70% by 2050.[112]

The Saline Water Conversion Corporation of Saudi Arabia provides 50% of the municipal water in the Kingdom, operates a number of desalination plants, and has contracted $1.892 billion[125] to a Japanese-South Korean consortium to build a new facility capable of producing a billion liters per day, opening at the end of 2013. They currently operate 32 plants in the Kingdom;[126] one example at Shoaiba cost $1.06 billion and produces 450 million liters per day.[127]

Lanzarote is the easternmost of the autonomous Canary Islands, which are of volcanic origin. It is the closest of the islands to the Sahara desert and therefore the driest, and it has limited water supplies. A private, commercial desalination plant was installed in 1964. to served the whole island and enable the tourism industry. In 1974, the venture was injected with investments from local and municipal governments, and a larger infrastructure was put in place in 1989, the Lanzarote Island Waters Consortium (INALSA)[130] was formed.

Barcelona 200,000 m3/day (operator Degremont) El Prat, near Barcelona, a desalination plant completed in 2009 was meant to provide water to the Barcelona metropolitan area, especially during the periodic severe droughts that put the available amounts of drinking water under serious stress.

The desalination plant located near La Rosière, Corbiere, Jersey, is operated by Jersey Water. Built in 1970 in an abandoned quarry, it was the first in the British Isles.

The original plant used a multistage flash (MSF) distillation process, whereby seawater was boiled under vacuum, evaporated and condensed into a freshwater distillate. In 1997, the MSF plant reached the end of its operational life and was replaced with a modern reverse osmosis plant.

Its maximum power demand is 1,750 kW, and the output capacity is 6,000 cubic meters per day. Specific energy consumption is 6.8 kWh/m3.[142]

El Paso: Brackish groundwater has been treated at the El Paso, Texas, plant since around 2004. It produces 27,500,000 US gallons (104,000,000 l; 22,900,000 imp gal) of fresh water daily (about 25% of total freshwater deliveries) by reverse osmosis.[145] The plant's water cost—largely representing the cost of energy—is about 2.1 times higher than ordinary groundwater production. On average, the plant produces 3.5 million gallons per day (about 11 acre-feet) at an average production cost of $489 per acre-foot.[146]

California has 17 desalination plants in the works, either partially constructed or through exploration and planning phases.[147] The list of locations includes Bay Point, in the Delta, Redwood City, seven in the Santa Cruz / Monterey Bay, Cambria, Oceaneo, Redondo Beach, Huntington Beach, Dana Point, Camp Pendleton, Oceanside and Carlsbad.

Carlsbad: The United States' largest desalination plant is being constructed by Poseidon Resources and is expected to go online 2016.[148] It is expected to produce 50 million gallons a day to 110,000 customers in San Diego County at an estimated cost of $1b.

Concord: Planned to open in 2020, producing 20 million gallons a day.

Monterey County: Sand City, two miles north of Monterey, with a population of 334, is the only city in California completely supplied with water from a desalination plant.

Santa Barbara: The Charles Meyer Desalination Facility[149] was constructed in Santa Barbara, California, in 1991–92 as a temporary emergency water supply in response to severe drought. While it has a high operating cost, the facility only needs to operate infrequently, allowing Santa Barbara to use its other supplies more extensively.

In 1977 Cape Coral, Florida became the first municipality in the United States to use the RO process on a large scale with an initial operating capacity of 3 million gallons per day. By 1985, due to the rapid growth in population of Cape Coral, the city had the largest low pressure reverse osmosis plant in the world, capable of producing 15 MGD.[150]

As of 2012, South Florida has 33 brackish and two seawater desalination plants operating with seven brackish water plants under construction. The brackish and seawater desalination plants have the capacity to produce 245 million gallons of potable water per day.[151]

Tampa Bay: The Tampa Bay Water desalination project near Tampa, Florida, was originally a private venture led by Poseidon Resources, but it was delayed by the bankruptcy of Poseidon Resources' successive partners in the venture, Stone & Webster, then Covanta (formerly Ogden) and its principal subcontractor, Hydranautics. Stone & Webster declared bankruptcy June 2000. Covanta and Hydranautics joined in 2001, but Covanta failed to complete the construction bonding, and then the Tampa Bay Water agency purchased the project on May 15, 2002, underwriting the project. Tampa Bay Water then contracted with Covanta Tampa Construction, which produced a project that failed performance tests. After its parent went bankrupt, Covanta also filed for bankruptcy prior to performing renovations that would have satisfied contractual agreements. This resulted in nearly six months of litigation. In 2004, Tampa Bay Water hired a renovation team, American Water/Acciona Aqua, to bring the plant to its original, anticipated design. The plant was deemed fully operational in 2007,[38] and is designed to run at a maximum capacity of 25 million US gallons (95,000 m3) per day.[152] The plant can now produce up to 25 million US gallons (95,000 m3) per day when needed.[153]

The Republic of Trinidad and Tobago uses desalination to open up more of the island's water supply for drinking purposes. The country's desalination plant, opened in March 2003, is considered to be the first of its kind. It was the largest desalination facility in the Americas, and it processes 28,800,000 US gallons (109,000 m3) of water a day at the price of $2.67 per 1,000 US gallons (3.8 m3).[156]

This plant will be located at Trinidad's Point Lisas Industrial Estate, a park of more than 12 companies in various manufacturing and processing functions, and it will allow for easy access to water for both factories and residents in the country.[157]

Evaporation of water over the oceans in the water cycle is a natural desalination process.

The formation of sea ice is also a process of desalination. Salt is expelled from seawater when it freezes. Although some brine is trapped, the overall salinity of sea ice is much lower than seawater.

Seabirds distill seawater using countercurrent exchange in a gland with a rete mirabile. The gland secretes highly concentrated brine stored near the nostrils above the beak. The bird then "sneezes" the brine out. As freshwater is not usually available in their environments, some seabirds, such as pelicans, petrels, albatrosses, gulls and terns, possess this gland, which allows them to drink the salty water from their environments while they are hundreds of miles away from land.[158][159]

Mangrove trees grow in seawater; they secrete salt by trapping it into parts of the root, which are then eaten by animals (usually crabs). Additional salt removal is done by storing it in leaves which then fall off. Some types of mangroves have glands on their leaves, which work in a similar way to the seabird desalination gland. Salt is extracted to the leaf exterior as small crystals, which then fall off the leaf.